1. Field of the Invention
The present invention relates to a moisture absorbing fiber. More particularly, it relates to a moisture absorbing fiber having high whiteness and an excellent color stability showing an excellent processing ability in spite of its anti-inflammability and antibacterial property, having further improved whiteness as compared with the conventional products and showing almost no color change even when bleaching treatment during dyeing step and washing are repeated.
2. Description of the Related Art
As a means for removal of moisture from air using fibrous materials, there has been proposed a means of Japanese Patent Laid-Open No. 01/299,624 where a deliquescent salt is impregnated with a highly water-absorbing fiber. The fiber obtained by such a means has practical properties that it is easy for making into knitting, textile, nonwoven fabric, etc., has quick moisture absorbing and desorbing rates and shows no detachment of moisture absorbent. However, its fiber surface is hydrogel and, therefore, it becomes tacky upon absorption of moisture, its application especially to wall paper and cotton fillings for bedclothes is difficult and it does not satisfy anti-inflammability and antibacterial property which have been increasing as social demands.
As a means for solving such problems, there has been a proposal for a means of Japanese Patent Laid-Open No. 05/132,858. However, in such a method, when amount of salt-type carboxyl group is more than 4.5 meq/g, tensile strength becomes 0.9 cN/dtex or less which is an insufficient fiber property for subjecting to various treatments and that is obstacle for further increase of hygroscopicity. When an increase in nitrogen content introduced by the treatment with a hydrazine compound for preparing a highly moisture-absorbing fiber where fiber strength is 0.9 cN/dtex or more is made more than 8.0% by weight, there is a problem that amount of introduction of salt-type carboxyl group after hydrolysis becomes little whereby hygroscopicity becomes low.
There is another disadvantage that the fiber obtained by the method of Japanese Patent Laid-Open No. 05/132,858 shows dark pink color to dark brown color and, therefore, field in which the fiber is able to be utilized is limited. In the invention for Japanese Patent Laid-Open No. 09/158,040 which has been proposed for overcoming such a disadvantage, there is disclosed that an acidic treatment A is carried out after the cross-linking treatment using a hydrazine compound and that an acidic treatment B is carried out after the hydrolyzing treatment with an alkali whereby considerable improvement in whiteness can be achieved. However, the current status is that even such an art is unable to give sufficient satisfaction to the field where a strict whiteness is demanded. In Japanese Patent Laid-Open No. 2000/303,353, there is disclosed a method for improving the whiteness where the hydrolyzing treatment is carried out in a non-oxygen atmosphere. However, the current status is that the fiber obtained by the said method is colored when oxidative bleaching treatment during dyeing step and washing are repeated and, therefore, it has a disadvantage of poor color stability.
An object of the present invention is to provide fiber in which the disadvantage that color is unstable in such conventional moisture absorbing fibers is improved where basic physical property demanded to fiber and characteristic to be owned by moisture-absorbing fiber are still maintained and also to provide a method for the manufacture of such a fiber.